Method of forming teeth in gear blanks



Nov. 24, 1931. c. G. OLSON 1,833,227

METHOD OF FORMING TEETH IN GEAR BLANKS Original FiledvMarch 25, 1927 2Sheets-Sheet 1 i I jww= 6: 055m Nov. 24, 1931. c. G. OLSON METHOD OFFORMING TEETH INGEAR BLANKS Original Filed March 25. 1927 2' Shee'tsk-Shee 2 v w, l v. 3 m M 6 0 v MY x M m-W af A 3 v M W J v is PatentedNov. 24, 1931 CARL OLSON, OF CHICAGO, ILLINOIS, ASSIGNOR TO rumors r001.worms,

CHIGAGO, ILLINOIS, A CORPORATION OF ILLINOIS METHOD OF FORMIN G TEETH INGEAR BLANKS I Original application filed March 25, 1927, Serial No.178,248. Divided and this application filed January 11,

1930. Serial My present invention relates to improve ments in methods ofcutting teeth in gear blanks and this application is a division of mycopcnding application which relates to improvements in hobs, Serial No.178,248,

iilcd March 25, 1927.

It is one of the primary objects of my present invention to provide animproved practical and simple method whereby involute teeth may be cutin gear blanks in a very expeditious manner and to this end I propose topractice a method wherein a rotating gear blank may be engaged by acutting edge which is angularly disposed with respect to the gear blankso as to facilitate the cutting of the gear teeth.

Another and more specific object of my invention is to provide animproved method for cutting ,involute gear teeth wherein the marginalportions of a rotating gear blank may be successively engaged by cuttingedges, one of which leads the other in its cut-ting action and is alsocapable of removing more stock.

These and numerous other objects and advantages will be more apparentfrom the following detailed description when considered in connectionwith the accompanying drawings, wherein:

[is representative of a cutting tool by means of which my improvedmethod of cutting in. volute gear teeth may be effectively practiced;

Figure 2 is a side view of said hob; Figure 3 is a diagram on anincreased scale showing an outline of teeth of a gear and the teethofthe hob shown in Figures 1 i and 2;

Figure 4 is a-diagram analogous to Figure 3 showing the same gear teethin cooperative relation with teeth of an ordinary cutter or hob, thisview being shown to more clearly 45. set forth the manner in which myimproved method of cutting gear teeth differs from methods which haveheretofore been praticed; i

Figure 5 isa diagram showing an outline or profile of a tooth of the hobshown in Fig- Figure 1 is an end view of a hob which f will slantbackward from this line.

ures l to 3 inclusive to more clearly set forth the teachings of thepresent invention;

Figure 6 is a diagram analogous to Figure 5 and discloses an outline ofan ordinary hob tooth and the manner'in which it generatesas teeth ofsubstantially the same size and shape;

Figure 7 is a sectional view on the curved line 77 of Figure 1, thescale however being enlarged; and

Figure 8 is similar to Figure 20a a decreased scale but showing a doublethread hob instead of one having a single thread.

Referring now to the drawings more in detail wherein like numerals havebeen employed to designate similar parts throughout the various views,it is to be noted that for the purpose of illustrating one practicalapplication'of my invention, I have shown a hob or cutter by means ofwhich my improved method of gear teeth cutting may be practiced. Thishob has a body 10 with-teeth 12 arranged helically in accordance withthe general principles of a hob. In Figure 2 I have shown a singlethread hob, although the same principles apply to a double thread hob asshown in Figure 8. The drawings illustrate right hand hobs, that is, onein which the helix progresses from the right end to the left end whenthe hobis viewed from the side where the cutting edges face downward.The gashes 151, while extending approximately transversely of the threadhelix of the hob, extend helically and in a right-hand direction. Theresult is that the teeth are'rendered more acute at the leading edge 16(see especially Figure 7 with a corresponding decrease in the acutenessof the leaving edge 17. In fact the leaving edge becomes an obtuseangle. The effect produced upon the top cutting edge 18 is to give to itan obliquity with respect to the direction in which it moves in cutting,with the result that it will take a shearing cut. In my hob the teethare also undercut, by which I mean, as stated, that if a radial line bedropped from the top of the hob' tooth at the forward edge, the frontface of the teeth This produces what is termed hook and promotes theease with which the metal in the gear 100 ,topcutting edge 18, as

by running sented by the area, d, e, f.

blank may be cut. This undercutting also re. sults in an increase in theacuteness of the previously mentioned. From the foregoing it will beevident that the gashes alon a helix of the same hand lead as the threadhelix, the leading edge of the hob teeth has been made sharper, that is,rendered more acute, but at the expense of the leaving edge 17. Toconsider now the manner in which I have compensated for this referenceshould be had to the diagrams, particularly Figures 5 and 6. In theordinary hob,whose action is illustrated in Figure 6, the leaving edge17a removes a greater volume of metal from the gear blank than does'theleading edge 16a. Ordinarily the ratio is, roughly speaking, in theproportion of 30% to 20%, the remaining 50% being removed by the cuttingedge 18a at the top of the tooth. This is roughly illustrated in Figure6 wherein 21 represents the gear blank and 1211 the tooth of an ordinaryhob. The zone of action of the leading edge is represented by the areaa, b, a while the zone of action of the leaving edge 17a is repre- Thezone of action of the cutting edge 18a at the top of the hob tooth isrepresented by the area 6, b, c, f. It will be understood that thediagram is not offered as mathematically accurate, but as illustrative,and it will also 'be understood that these proportions will varyslightly under different conditions, for example, the volumes removed bythe diiferent cutting edges will be different where the gear is designedon a 14 pressure angle than where the gear is designed on a 20 pressureangle. The fact remains, however, that in practicing conventionalmethods with the ordinary hob, the

' about15%. As in the previous instance,

\ ing accurate leaving cutting edge is required to remove a considerableproportion of the total amount to be removed, and in practicing myimproved method, the amount of stock required to be removed by theleaving edge is much re-.

duced.

Referring now for comparison to the diagram of Figure 5 in which theprinciple of action of my hob is illustrated, the leading edge 16removes metal from the zone A, B, C while the volume whichmust beremoved by the leaving edge 17 is represented by the area D, E, F. Thevolume removed by the top cutting edge 18 is represented by the area E,B, C, F. Roughly speaking, for hobs designed to produce involute gearteeth based on a 20 pressure angle the volume of metal removed by theleading ed e of'my hob will be ordinarily in the neigh orhood of 25% ofthe whole, and of the top cutting edge about 50% of *the'whole, and ofthe leaving Iedge owever, these percentages are not offered as bebutrather as beingillustrative,

and the same is true of the diagram itself.

' Now to explain the difference in the two teeth 21 are identical.

hobs of Figures 5 and 6 and the methods capable of being practicedthereby more from the theoretical viewpoint, attention is directed toFigures 3 and 4, which are also diagrammatic and show respectively thenew and the ordinary hob. In these two views the gear The pitch circleof the gear teeth is represented by the are 30, and the pressuretailgcnt by the line 31 which may be assumed to be at an angle of 20from-the radius 32 which passes through the pressure point 34, thatis,.the point where the pressure tangent intersects the pitch circle.The

base circle 36 from which the gear tooth is between this and the pitchline tangent 39 of the gear will, of course, represent the pressureangle. In the ordinary hob, which F igure 4 represents, the side of theadjacent hob tooth is made to conform (allowance being made forclearance of course) to the pressure tangent 31. Thus the hob teeth willhave the same pressure angle as the teeth of the gear to be cut.

Now referring for comparison to Figure 3,'which is adiagram illustratingthe action of my improved hob, the gear teeth 21 are the same as inFigure 4, and the same is true of the pitch circle 30, pressure gearteeth and gear tooth tangent 39. But for my hob I make the side of thehob tooth conform to a pressure tangent 31a which is tangent to the sideof the gear tooth at a oint 40 lower down on the gear. tooth. Thus itWill be evident that the teeth of my new hob will havesides which aremore nearly perpendicular to the hob axis, and are thinner at thebase'and thicker at the top than the teeth of the ordinary'hob shown inFigure4.

A perpendicular 38a erected upon a line 31a at the point 40 will liemore nearly parallel with the pitch'line 42 of the hob than will line 38relatively to the pitch line tangent 39 of the gear. Thus, angle issmaller and the pitch line 42 of the hob is not coincident with thepitch line tangent 39 of the gear. Incidentally it may be stated that inmy hob the lead is somewhat shorter than in the ordinary hob.

. The hob shown in Figure 8 is made in accordance with the principlesabove described, but has a double thread, that is, having two starts ofthread, which is found to be desiralhia, especially in connection withroughing From the foregoing it will be seen that my hob in its preferredform has two cutting edges which are definitely acute, but that whilethis acuteness-is obtained at the expense of the third cutting-edge,which becomes obtuse, this objection is more than offset by the improvedaction of the othertwo cuttingedges line 38 of the in my hob thepressure ordinary hobs are used. The improvement becomes very importantwhen cutting gear teeth oflarge pitches where the bulk of the materialis removed by a roughing operation, for

which this hob is far superior to the 'ordi- .series of cutting naryroughing hob.

v From the foregoing it will be understood that in practicing myimproved method of cutting gears, the gear blank is rotated and a edgesare successively brought into engagement with the marginal portionthereof. edges are arranged in'pairs as clearly set forth above indescribing the specific hob construction by means of which my method maybe practiced. Each pair of cutting edges,

namely edges'16 and 17, are inclined toward each other, and the angleincluded between said edges is less than twice the pressure angle of thegear to be cut. This is clearly evident from the diagram shown in Figure3 wherein the angle formed by the pressure tangent 3laand an imaginaryline forming the extension of the opposite side of the hob tooth is lessthan the angle which would be included between companion pressuretangents of the gear teeth. In other words, by referring specifically tothe hob, it may be said that the pressure angle of the hob teeth is lessthan the pressure angle of the gear teeth which are cut.

Having thus described my invention, what I claimas new and desire tosecure by Letters Patent is: i

1. The method of forming involute teeth in gear-blanks which consists inrotating the gear blank and successively engaging'the marginal portionof the blank with pairs of cutting edges, one of the edges in each pairleading the other in its cutting action, said cutting action being suchas to remove more stock by the leading cutting edges of each pair thanthe other edges.

2. The method of forming involute teeth in gear blanks which consists inrotating the gear blank, moving pairs of cutting edges about a commonaxis, one of the cutting edges in each pair leading the other, andsuccessively engaging the mar inal portions of the blank with said pairsof cutting edges so as to remove more stock by the leading cutting edgesthan the other edges.

The method of forming involute gear teeth in gear blanks which consistsin re- These series of cutting included angle in gear blanks whichconsistsin rotating the gear blank and successively engaging themarginal portion of said blank with pairs of cutting edges, one of theedges in each pair constituting a leading edge which is sharper than theother edge, whereby stock may be more readily removed by said leadingedges than by the other edges.

5. The method of forming involute teeth in gear blanks which consists inrotating the gear blank and successively engaging the marginal portionof said blank with pairs of angularly disposed cutting edges, the angleincluded between the cutting edges of each pair being less than twicethe pressure angle in each pair being sharper than its companion edgeand leading the same in its cutting action, whereby stock may be morereadily removed by the leading cutting edges than the other cuttingedges.

6. The method of forming involute teeth in gear blanks which consists inrotating the gear blank and successively engaging the marginal portionof the blank with pairs of cutting edges, one of which leads the otherin cutting, said cutting action being in conformity with the moldinggenerating action of a rack having a pitch to conform with a generatingcircle of smaller diameter than the pitch circle in the gear to be cut,whereby the material to be removed in the gear blank is more unevenlydistributed between the cutting edges, and employing one of the edges ineach pair to remove a greater portion of the stock, said edgebeingsharper than the other companion edge to facilitate compliance withthis requirement.

7. The method of forming involute teeth in gear blanks which consists inrotating the blank and successively engaging the marginal portion ofsaid blank with pairs of cutting edges rotating in unison with eachother about a common axis, the cutting edges of the pair, when viewed indiametral section, being oblique with reference to each other and thebeing less than twice the pressure angle of the gear to be cut, theincluded angle at the front of the leading cutting edge, when consideredin coaxial cylindrical section, being an acute angle'and the includedangle at the front of the leaving edge being greater than at the leadingedge.

8. The method of forming involute teeth in gear blanks which consists inrotating the blank and successively engaging the marginal portion ofsaid blankwith pairs of cutting edges rotating in unison with each other.of the gear to be out, one of the cutting edges about a common axis,the cutting edges of the pair, when viewed in diametral section, beingoblique with reference to each other and the included angle being lessthan twice the pressure angle of the gear to be cut, the included angleat the front of the leading cutting edge, when considered in coaxialcylindrical section, being an acute angle and the included angle at thefront of the leaving edge being scribed my name.

an obtuse angle.

9. The method of cutting a gear which consists in employing a hobprovided with cuttingdeeth arranged in a thread, the sides of said teethhaving a slope of such'steepness as to cause them to generate on acircle of smaller diameter than the diameter of" the pitch circle of thegear to be cut, rotating the hob on its axis, and causing the teeththereof to successively engage the margin of a gear blank.

In witness whereof, I have hereunto sub- CARL e. OLSON}

